1. Field of the Invention
The present invention relates to optical window members, and more particularly to an optical window member arranged on the front side of a solar battery.
2. Description of the Related Art
There are products with a built-in solar battery used as a power source. For example, there are watches with a solar battery arranged behind the dial plate. In such a watch, an optical window member is provided on the front side of the solar battery so that the solar battery is not visible and to enhance decorative effects. It is important that the power generation efficiency of the solar battery not be decreased by the optical window member any more than necessary.
As shown in FIG. 1, a conventional optical window member includes a glass substrate 1 on which a shielding layer 2 that diffuses light reflected from a solar battery 10 so as to reduce the amount of light irradiated upward, an interference filter 3, and a diffusing layer 4 that diffuses light reflected from the solar battery 10 are arranged. The solar battery 10 is formed underneath the glass substrate 1 by forming an amorphous silicon film by a PCVD (plasma-activated chemical vapor deposition) method.
The solar battery is not visible when the optical window member is viewed from the top, and power is efficiently generated from the solar battery.    Patent Document 1: International Application Publication No. WO95/12897
However, the above described optical window member includes three layers on the glass substrate 1, namely the shielding layer 2, the interference filter 3, and the diffusing layer 4. Accordingly, it is difficult to reduce manufacturing costs.